[pure-silver] Re: Opinion Please!


----- Original Message ----- From: "Eric Neilsen Photo" <ej@xxxxxxxxxxxxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, November 22, 2009 7:33 PM
Subject: [pure-silver] Re: Opinion Please!


I recall this formula being different than that available from PF. I don't recall the specific though. The formulary required quite a bit of specific mixing. I tried to get Bryant labs to offer up the Aminophenol Hydrochoride CAS # 123-30-8, but they went out of business shortly after I asked them.



Eric

There are several versions of the Rodinal formula but all are similar. Paraminophenol is related to Metol but was considered inferior to it. It has the virtue, as far as Rodinal anyway, of being soluble in considerable concentration. The formulas for Rodinal differ somewhat in the alkali specified but the commercial stuff, at least in recent decades, used potassium hydroxide. That is also soluble in high concentration. The paraminophenol appears to be dissolved just to the point of supersaturation. However, the commercial product before its discontinuance did not have any crystals in it although I am told the earlier solutions did. While Rodinal works well for many films its main quality being convenience and being adjustable over a wide range of activity. However, it tends to be grainy and will not produce quite as much speed as, say, D-76. Since the exact formula and method of manufacture were proprietary it is an open question if similar products made by Calbe or Photographer's Formulary are really the same as the original AGFA prduct. BTW, the reason AGFA used potassium salts so often in their formulae appears to be that they produced enormous amounts of potassium as a by-product of their chemical manufacturing operations.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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